1. Field of the Invention
The present invention generally relates to a battery voltage monitor circuit, such as a battery voltage monitor circuit for monitoring voltages of multiple secondary batteries connected in series.
2. Description of the Related Art
In recent years, a secondary battery (e.g., lithium ion battery) is used as a power source mounted on a vehicle such as an electric-powered bicycle or an automobile. The lithium ion battery is to be equipped with a monitor circuit for monitoring the voltage of the lithium ion battery. In a case of using a single battery pack having multiple lithium ion batteries connected in series, the monitor circuit accurately measures the voltage of each of the multiple lithium ion batteries and notifies the measurement result to an upper level device such as an external CPU (Central Processing Unit).
A protection apparatus and a condenser of a module battery having multiple secondary batteries connected in series according to a related art example (see, for example, Japanese Laid-Open Patent Publication No. 2001-177998) includes a first protection unit that detects a voltage between terminals of the secondary batteries and outputs a signal to stop the charging/discharging of the module battery in a case where the detected voltage of the terminals of the secondary batteries is beyond a predetermined range, and a second protection unit that detects a voltage between terminals of the module battery and outputs a signal to stop the charging/discharging of the module battery in a case where the detected voltage of the terminals of the module battery is beyond a predetermined range.
Although battery voltage monitor circuits that monitor the voltage of a battery pack are expected to have high reliability, the reliability of the battery voltage monitor circuits may be degraded by harsh environmental usage conditions (e.g., temperature, vibration) in a case where the battery pack is mounted on a vehicle.
As one method for improving reliability of the battery voltage monitor circuits under a harsh environmental usage conditions, there is a method of dualizing the battery voltage monitor circuit mounted on the battery pack. However, this dualizing method has a problem of doubling the cost of the battery voltage monitor circuit.